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• A typical and common herbaceous plant of Neyraudia reynaudiana roots was selected as the research objective. • The effect of both moisture content and root density to root-soil complex are discussed. • Roots could enhance the soil shear strength mainly reflected in the increase of cohesive force. • Moisture content was introduced into the shear strength model of root-soil complex. The collapse of collapsing walls is a key process during the Benggang development in southeast China and is closely related to the soil shear strength. Plant root reinforcement can effectively improve the soil shear strength. However, there are few studies on the effect of roots on the soil shear strength of collapsing walls. To explore the influence of roots on the soil shear strength of collapsing walls, the roots of Neyraudia reynaudiana was selected as the research object. This paper studies the tensile properties of the roots through root tensile tests and performs a direct shear test to study the influence of the roots on the soil shear strength by setting different mass moisture contents (15%∼30%) and root weight densities (0 ∼ 1.25 g 100 cm−3). Root tensile force is positively correlated with root diameter by a power function, while tensile strength is negatively correlated with diameter by a power function. Roots could increase the soil shear strength, and which was mainly reflected in cohesive force. The shear strength and cohesive force increase first then decrease with the increasing root density, while root density has no effect on the internal friction. The shear strength, cohesive force and internal friction of root-soil complex all decreased with increasing moisture content. The WWM (Wu and Waldron model) greatly overestimated the cohesion of herbaceous roots, and a new prediction model of the shear strength of root-soil composites was obtained by revising the WWM model by introducing the moisture content and root density (NSE = 0.94). In conclusion, Neyraudia reynaudiana roots could improve the soil shear strength, whereas the strengthening effect decreased under the condition of high moisture content. The results provide a basis for the selection and allocation of vegetation restoration measures in Benggang erosion in southern China. [ABSTRACT FROM AUTHOR]

[Display omitted] • FTCs weakened the shear strength and disintegration resistance of the soil. • Increase of water and salt content exacerbated soil erosion due to FTCs. • The effect of FTCs on soil microstructure was investigated. • The underlying micro-mechanism of the change in soil erodibility was explored. Soda-saline loessal soils are distributed extensively in the Songnen Plain of Northeast China. Freeze-thaw effects on soil structure and mechanical properties are becoming more frequent and intense with global warming, which further affects soil erosion in cold regions. Quantifying the effects of freeze-thaw cycles (FTCs) on the erodibility of saline soils is challenging because of the abundant soluble salt content and complex soil mechanical responses. In this study, direct shear tests, disintegration tests, and scanning electron microscopy were conducted to investigate the effects of freeze-thaw action on the erodibility indicators (shear strength and disintegration velocity) of soda-saline loessal soils and their microscopic deterioration mechanisms. Four initial moisture contents (IMCs: 8%, 13%, 18%, 23%), three soluble salt contents (SSCs: 0.5%, 1.0%, 1.5%), and six FTCs (0, 1, 3, 6, 10, 15) were considered. The results showed that successive FTCs continued to degrade the erosion resistance of the soil until it stabilized after approximately 10 FTCs. After 15 FTCs, the shear strength and cohesion decreased by 8.6–19.8% and 24.1–59.2%, respectively, while the angle of internal friction was relatively unaffected. Meanwhile, the soil disintegration velocity increased by 52.3–208.8%. During the freeze-thaw process, the water-ice phase change and the crystallization of soluble salts both led to the continuous adjustment of the microstructure of soda-saline loessal soils. It was found that microcracks within the soil structural units increased significantly, cementation between the structural units weakened continuously, pore connectivity was enhanced, and pore size homogenization increased. Correlation analysis showed that IMC was the fundamental factor affecting the soil mechanical properties, whereas SSC mainly affected the soil's resistance to disintegration. The increase in IMC and SSC exacerbated the deterioration of the soil by freeze-thaw action. This paper presents a new understanding of the erosion characteristics and micromechanisms of soda-saline loessal soils in seasonally frozen regions under freeze-thaw action. [ABSTRACT FROM AUTHOR]

[Display omitted] • FTCs weakened the shear strength and disintegration resistance of the soil. • Increase of water and salt content exacerbated soil erosion due to FTCs. • The effect of FTCs on soil microstructure was investigated. • The underlying micro-mechanism of the change in soil erodibility was explored. Soda-saline loessal soils are distributed extensively in the Songnen Plain of Northeast China. Freeze-thaw effects on soil structure and mechanical properties are becoming more frequent and intense with global warming, which further affects soil erosion in cold regions. Quantifying the effects of freeze-thaw cycles (FTCs) on the erodibility of saline soils is challenging because of the abundant soluble salt content and complex soil mechanical responses. In this study, direct shear tests, disintegration tests, and scanning electron microscopy were conducted to investigate the effects of freeze-thaw action on the erodibility indicators (shear strength and disintegration velocity) of soda-saline loessal soils and their microscopic deterioration mechanisms. Four initial moisture contents (IMCs: 8%, 13%, 18%, 23%), three soluble salt contents (SSCs: 0.5%, 1.0%, 1.5%), and six FTCs (0, 1, 3, 6, 10, 15) were considered. The results showed that successive FTCs continued to degrade the erosion resistance of the soil until it stabilized after approximately 10 FTCs. After 15 FTCs, the shear strength and cohesion decreased by 8.6–19.8% and 24.1–59.2%, respectively, while the angle of internal friction was relatively unaffected. Meanwhile, the soil disintegration velocity increased by 52.3–208.8%. During the freeze-thaw process, the water-ice phase change and the crystallization of soluble salts both led to the continuous adjustment of the microstructure of soda-saline loessal soils. It was found that microcracks within the soil structural units increased significantly, cementation between the structural units weakened continuously, pore connectivity was enhanced, and pore size homogenization increased. Correlation analysis showed that IMC was the fundamental factor affecting the soil mechanical properties, whereas SSC mainly affected the soil's resistance to disintegration. The increase in IMC and SSC exacerbated the deterioration of the soil by freeze-thaw action. This paper presents a new understanding of the erosion characteristics and micromechanisms of soda-saline loessal soils in seasonally frozen regions under freeze-thaw action. [ABSTRACT FROM AUTHOR]